alike. Besides thus
interpreting the formations of Russia, England, and America, Sir R.
Murchison thus interprets those of the antipodes. Fossils from Victoria
Colony, he agrees with the Government-surveyor in classing as of Lower
Silurian or Llandovery age: that is, he takes for granted that when
certain crustaceans and mollusks were living in Wales, certain similar
crustaceans and mollusks were living in Australia. Yet the
improbability of this assumption may be readily shown from Sir R.
Murchison's own facts. If, as he points out, the fossil crustaceans of
the uppermost Silurian rocks in Lanarkshire are, "with one doubtful
exception," all "distinct from any of the forms known on the same
horizon in England;" how can it be fairly presumed that the forms
existing on the other side of the Earth during the Silurian period, were
nearly allied to those existing here? Not only, indeed, do Sir R.
Murchison's conclusions tacitly assume this doctrine of universal
distribution, but he distinctly enunciates it. "The mere presence of a
graptolite," he says, "will at once decide that the enclosing rock is
Silurian;" and he says this, notwithstanding repeated warnings against
such generalizations. During the progress of Geology, it has over and
over again happened that a particular fossil, long considered
characteristic of a particular formation, has been afterwards discovered
in other formations. Until some twelve years ago, Goniatites had not
been found lower than the Devonian rocks; but now, in Bohemia, they have
been found in rocks classed as Silurian. Quite recently, the
_Orthoceras_, previously supposed to be a type exclusively palaeozoic,
has been detected along with mesozoic Ammonites and Belemnites. Yet
hosts of such experiences fail to extinguish the assumption, that the
age of a stratum may be determined by the occurrence in it of a single
fossil form. Nay, this assumption survives evidence of even a still more
destructive kind. Referring to the Silurian system in Western Ireland,
Sir R. Murchison says, "in the beds near Maam, Professor Nicol and
myself collected remains, some of which would be considered Lower, and
others Upper, Silurian;" and he then names sundry fossils which, in
England, belong to the summit of the Ludlow rocks, or highest Silurian
strata; "some, which elsewhere are known only in rocks of Llandovery
age"--that is, of middle Silurian age; and some, only before known in
Lower Silurian strata, not far a